In electric circuits, the conductors are generally electrically insulated and spaced from one another by a plurality of electrical insulators. When the conductors are at different alternating or continuous potentials, there is created about the insulators, an electric field in which the distribution thereof in space varies in accordance with the geometry of the interconnection, the differential in potential, and the composition of materials utilized. If there is a fault inside the insulator or at its surface, then the distribution of the electric field will be affected or perturbed in the area of the fault.
Devices have been developed to verify the condition of porcelain type insulators of the type having a plurality of porcelain bushings interconnected to one another in series to form a chain. Each element in the chain is verified independently and individual defective ones can be identified. However, with respect to continuous insulators which have a single continuous insulating core, such as a body or rod-like element of porcelain or fiberglass that may be covered with insulating material, no adequate means has heretofore been developed to verify its integrity. This is particularly so with composite insulators which are formed of a single rod-like insulating core as the risks are higher when there is a defect as compared to the porcelain chain type insulating devices as aforementioned where one or several elements in the chain can fail without presenting serious inconvenience to the insulator or maintenance personnel if these are detected early. The lack of means to verify the condition of composite insulators has caused hesitation on the part of contractors to use such devices. In fact, the lack of proper testing apparatus has resulted in the lack of data concerning the life expectancy of composite insulators. There is also a need to verify the uniformity of these composite insulators at the manufacturing stage so that fabricators can provide adequate data on these composite insulators.
Because the composite insulator has a single continuous insulating core, such as a ceramic or fiberglass rod, a defect in the ceramic or fiberglass rod may not be detected and cause serious injury to an installer. In order to reduce this risk, there is a need to provide a portable test apparatus capable of performing a verification of the insulator prior to its installation and after it has been in service. A partially defective composite insulator could fail completely at the time when an operator is effecting maintenance work or installing the insulator between live wires. Although there is a small risk of such injury, this risk can be eliminated if proper test apparatus were provided. Currently composite insulators are verified only by sight and sound to reveal defects and this is very hazardous to the installers, the maintenance personnel, and to the H.V. distribution or transmission network incorporating such composite insulators.